1. Field of The Invention
The present invention relates to a filter medium for treating a blood material. More particularly, the present invention is concerned with a filter medium for treating a blood material, comprising a polymeric, porous element having a surface electric charge of not smaller than -30 .mu.eq/g of the polymeric, porous element. The filter medium of the present invention can advantageously be used for treating a blood material (to be used for, e.g., transfusion) without causing an increase in bradykinin concentration of the treated blood material to an unfavorable level (bradykinin is a cause of anaphylactic reactions in transfusion recipients). The present invention is also concerned with a blood-treating filter apparatus having the filter medium packed therein.
2. Discussion of Related Art
In recent years, in the field of blood transfusion, a leukocyte-free blood transfusion, in which leukocytes are removed from a blood material by means of a polyester non-woven fabric or a cotton fabric before the blood material is employed in transfusion, has increasingly been carried out. This is because it has been elucidated that side effects of transfusion, such as headache, nausea, chills and non-hemolytic feverish reaction, and side effects more serious to a recipient, such as allosensitization, post-transfusion GVHD (graft versus host disease) and viral infection, are mainly caused by leukocytes contained in the blood material employed for transfusion. Removal of leukocytes from blood is also conducted, using a filter material such as non-woven fabric or the like, for therapy of autoimmune diseases, such as systemic lupus erythematosus, chronic anticular rheumatism and multiple sclerosis; leukemia; cancer and the like, and for lowering the immune function of a patient prior to organ transplantation.
In the field of cardiac surgery, for example after a surgical operation for forming a coronary bypass, attempts are made to remove leukocytes from blood to be circulated to the patient. This is because leukocytes are likely to be activated at the site of the operation, and thereby emit superoxides which damage the site of the operation.
Further, after a surgical operation, blood obtained from a patient during the operation is sometimes recovered and returned to the operated patient. Such recovered blood is likely to be contaminated with tissue pieces, broken bone pieces, dust and the like, which are produced in during the operation of the patient. These contaminants are removed from the blood using a filter material before returning the blood to the patient. Furthermore, in adsorption-removal of an undesired substance from plasma by extracorporeal circulation of the plasma, a container with an adsorbent material packed therein is used. A filter medium is provided, not only at an outlet of the container, but also in a blood flow line downstream of the container, for preventing the adsorbent material or broken pieces thereof from leaking out of the container and blood flow line and, into the patient.
As the filter media for use in the above leukocyte-removing treatments, fibrous materials, such as cotton fabric or non-woven fabric, and porous materials having continuous pores, such as a sponge, are used, and various researches on these types of filter materials are made. The surfaces of these materials are generally treated so as to introduce an electrical negative charge thereto, so that hydrophilicity is imparted for increasing the wettability of the surfaces there of with blood.
In the fields of blood filtration, blood dialysis, plasma separation, plasma component filtration and the like, there are used membrane type filter media, such as hollow fiber membranes, flat membranes, or the like which are made of regenerated cellulose, polyacrylonitrile, polymethyl methacrylate, polysulfone, polyolefins, cellulose acetate and the like.
Furthermore, for removal or recovery of components of a body fluid, such as plasma, by adsorption-filtration, various types of adsorptive materials are used. Examples of adsorptive materials include an autoantibody-adsorptive material made of a porous polyvinyl alcohol substrate with tryptophane or phenylalanine immobilized thereon, a low density lipoprotein-adsorptive material made of a porous cross-linked cellulose substrate with dextran sulfate immobilized thereon, and an adsorptive material (for an antibody against an antiblood type substance) comprising a porous silica gel substrate with a saccharide immobilized thereon.
It is known that when blood is contacted with a material surface having an electrical negative charge, e.g. glass etc., blood coagulation factor XII in the blood is activated, so that kallikrein is produced from prekallikrein by the action of the activated blood coagulation factor XII. It is also known that the produced kallikrein causes endo-cleavage of high molecular weight kininogen at two internal sites thereof, to thereby produce a kinin (bradykinin). Further, it is known that the kinin is a substance which causes anaphylactic reactions, such as lowering of blood pressure, facial suffusion, conjunctival hyperemia, smooth muscle contraction, pain, etc., that is, the kinin is an anaphylatoxin. However, no quantitative study has been made with respect to the relationship between the production of kinin and the negative charge on the surface of a material. In particular, no investigation has been made with respect to an acceptable quantity of negative charge on the surface of a material for clinical use. Furthermore, no clinical knowledge has been obtained with respect to the relationships between the symptoms by anaphylactic reactions and the quantity of kinin.